The invention relates to novel catalysts for hydrocarbon conversion processes, particularly polymerization and oligomerization processes.
In the refining of hydrocarbon containing feedstocks, it is often necessary to convert hydrocarbon compounds contained in the feedstock to different forms. Typically, particulate catalysts are utilized to promote chemical reactions when feedstocks contact such catalysts under hydrocarbon conversion conditions to produce economically upgraded hydrocarbon products.
An on-going aim of the art is to provide a catalyst having suitably high activity, stability and/or selectivity for a given product. Activity may be determined by comparing the temperature at which various catalysts must be utilized under otherwise constant processing conditions with the same feedstock so as to produce a given percentage of products boiling in a given temperature range. The lower activity temperature for a given catalyst, the more active such a catalyst is in relation to a catalyst of higher activity temperature. Alternatively, activity may be determined by comparing the percentages of conversion of feedstock reactants to products boiling in a given range when various catalysts are utilized under otherwise constant processing conditions with the same feedstock. The higher the percentage of product converted to the given boiling range for a given catalyst, the more active such a catalyst is in relation to a catalyst converting a lower percentage of the same feedstock reactants to the same products. Selectivity may be determined during the foregoing described activity test and is measured as the percentage of a given product boiling in a given temperature range. Stability is generally measured in terms of the change in temperature required per unit of time to maintain a given percentage of product, or alternatively, in terms of the change in percentage of product per unit of time. The lower the change in percentage of product per time unit for a given catalyst, the more stable such a catalyst is in relation to a catalyst yielding a greater change.
Catalytic oligomerization is a useful process for the conversion of relatively low molecular weight olefins into industrially important olefins of higher molecular weight. Solid phosphoric acid catalysts have been utilized for such operations. A typical catalyst is phosphoric acid supported on kieselguhr. Such a catalyst provides suitable oligomerization activity (i.e., percentage conversion of lower molecular weight olefins to liquid products containing higher molecular weight olefinic oligomers); however, the catalyst structurally degrades during processing which causes large pressure drops through the reactor vessel. Such pressure drops mandate frequent shut downs of the oligomerization process in order to replace the catalyst. Furthermore, degradation of the catalyst also causes a difficult catalyst unloading problem wherein hydrostatic drilling is often necessitated to remove the degraded catalyst from the internal surfaces of the reactor vessel.
The search continues for catalysts providing suitable hydrocarbon conversion activity and stability, particularly oligomerization activity and stability, and also improving the problem of unloading spent catalysts.